Add option to QXmlStreamWriter for enclose attribute values with single quote

An option to choose between single quoted or double quoted attribute values could be desirable.

With single quote, qDebug() logging facilities do not escape the quoting. Sure we can use qDebug("%s", ...); but it's remove advantages of using the qDebug() << ...;

Also, double quoting make the task of copying output of QXmlStreamWriter to paste it in a .cpp file more tedious unless escaped, but if escaped, the logging output become tedious to read.

"<?xml version=\"1.0\" encoding=\"UTF-8\"?><stream:stream xmlns=\"jabber:client\" xmlns:stream=\"http://etherx.jabber.org/streams\" id=\"id\" from=\"ex.com\" to=\"foo@ex.com\" version=\"1.0\" xml:lang=\"en\">"

vs

"<?xml version='1.0' encoding='UTF-8'?><stream:stream xmlns='jabber:client' xmlns:stream='http://etherx.jabber.org/streams' id='id' from='ex.com' to='foo@ex.com' version='1.0' xml:lang='en'>"

Yeah it's estheticism but I like estheticism